Buffer storage is a means of temporarily storing electrical energy or heat generated, for example, by solar or wind energy devices, so that it is available for later use. Electricity produced by solar modules or wind turbines can be stored in batteries. This means that a steady electric supply is still available even when the sun isn't shining or the wind blowing. Similarly, in the case of a solar heating systems, heat generated at the sunniest times of the day can be stored for short periods in a water storage tank or for longer periods in a long-term hot water storage tank.